Field
The disclosure relates generally to a buck controller and, more particularly, to a control method using inductor coil current estimation thereof.
Description of the Related Art
Voltage regulation is important where circuits are sensitive to transients, noise and other types of disturbances. The control of the regulated voltage is key in switched mode power supplies (SMPS) and in many hysteretic-based topologies. Switched mode power supply topologies include the buck converter topology.
In hysteretic-based topologies, one of the topologies includes a hysteretic current-mode (CM) topology.
FIG. 1 shows a typical hysteretic current-mode controller. The buck converter 100 consists of a SR flip-flop 105 with inputs SET 101 and RESET 102. The SR flip-flop 105 provides a DUTY signal output 107 to pre-drive circuitry 110. The signal VIN 115 provides power to the output circuit comprising of a p-channel metal oxide semiconductor field effect transistor (MOSFET) pull-up device 120 and an n-channel metal oxide semiconductor field effect transistor (MOSFET) pull-down device 125. The p-channel MOSFET can be referred to as a PMOS transistor, and the n-channel MOSFET can be referred to as a NMOS transistor. The center node VLX is connected between the p-channel MOSFET 120 and n-channel MOSFET 125 providing a current to the output. The output node is connected to the inductor 140, the output capacitor 145 for the output signal 150, and output load 160.
Both MOSes can be replaced with BJTs or any other types of semiconductor switches. PMOS can be replaced with NMOS and vice-versa
A feedback network establishes a sensing scheme to current sensing circuit 130. Current in the inductor coil 140 is measured via current sensing circuits CSp 135 and CSn 137 where CSp 135 is active when PMOS P is ON and CSn 137 is active when NMOS N is ON. Both signals from the current sensing circuits are combined in the Current Sensing Block 130 and produce one signal ILint 139 which is an internal replica in the current in the coil. The circuit contains an Error amplifier 170 with the output signal 165, reference signal 167 coupled to a compensation network. The output of the Error Amplifier 170 is coupled to a compensation network. The error amplifier compares the output voltage with the reference voltage Vref and generates error signal vError. This signal is a base for two signals vError_H 175A and vError_L 175B which are shifted up and down from the vError by Voff/2 respectively. Internal coil current replica ILint is then compared with the vError_H 175A and vError_L 175B signals and resets (signal 185A) and sets (signal 185B) the main RS Flip-Flop FF1 105 which controls the switches.
FIG. 2 shows the timing diagram 200 for the signals. The p-channel MOS (PMOS) 210 and n-channel MOS (NMOS) 220 shows the switching of the output stage. The signal vError_H 230 and vError 240, and vError_L 250 describes the switching states of the error compensation network. The current through the inductor ILint 260 is overlaid on the switching states. In order to keep the frequency within given range several techniques can be implemented. The same is true for discontinuous current mode (DCM) mode of operation where current in the coil doesn't go below zero.
The described topology in FIG. 1, is good during transient events. The disadvantage of this prior art embodiment is the high quiescent current due to dual current sensing circuit which causes lower efficiency at light loads. In addition, a second disadvantage is the current sensing circuitry are usually noisy and layout sensitive. Additionally, another disadvantage is that the current sensing circuitry can also introduce switching noise.
U.S. Patent Application 2014/0247026 to Svorc describes a switched mode power supply having increased efficiency due to a loss-less coil current estimation for current control using a capacitor that has the same signal shape as the current through the coil inductor.
U.S. Pat. No. 8,698,470 to Ju shows a buck voltage regulator with mode switching based on sensing an integrated inductor current sense signal with an integrated reference signal. The patent also discusses switching from PWM and PFM operation in a buck converter.
U.S. Pat. No. 8,766,617 to Wan et al describes a method for improving voltage identification transient response by sensing the inductor current of a voltage regulator.
U.S. Pat. No. 7,053,595 to Mei et al shows a method and circuit for compensating offset errors caused by propagation delays in hysteretic control loops.
U.S. Pat. No. 6,707,281 to Solivan describes a voltage regulator that may include an inductor and a current detection circuit to detect current through the inductor.
U.S. Pat. No. 6,037,754 to Harper shows a circuit with inductor maximum current computation, inductor current comparator, and a current magnitude sensor.
In these prior art embodiments, the solution to establish a sampling circuit in switching regulator utilized various alternative solutions.